Heretofore, reworking of printed circuit boards has involved desoldering solder bonds, removing integrated circuit chips, as necessary, and resoldering solder bonds. However, the requirements imposed upon microelectronics manufacturing by such developments as the development of high circuit density, high pin count devices with high populations of high I/O density on high circuit density packages, combined with no flux and no clean solder technologies, has imposed stringent requirements on solder process control.
One aspect of stringent process control is the exclusion of atmospheric oxygen from the molten solder, both in the solder pot and an the printed circuit card. Methods for restricting oxygen access to the molten solder in wave soldering apparatus are disclosed in, for example, U.S. Pat. No. 5,121,875 to Hagerty et al. for WAVE SOLDERING IN A PROTECTIVE ATMOSPHERE ENCLOSURE OVER A SOLDER POT, U.S. Pat. No. 5,121,874 to Deambrosio et al. for SHIELD GAS WAVE SOLDERING, U.S. Pat. No. 4,921,156 to Hohnerlein et al. for SOLDERING APPARATUS, and U.S. Pat. No. 4,538,757 to Bertiger for WAVE SOLDERING IN A REDUCING ATMOSPHERE. These patents describe various aspects of nitrogen blanketing of wave soldering during the original manufacture of printed circuit boards, including chip populating.
However, while the use of nitrogen blankets in the original manufacture of printed circuit boards is well known, there exists no teaching of soldering methods and tools for reworking pin-in-hole printed circuit boards that avoid oxidation of the solder and the workpiece during soldering. Nor is there any teaching of soldering methods and tools for reworking pin-in-hole printed circuit boards that permit the use of no-clean and even non-flux technology.